The prices for new hepatitis C and cancer treatments are driving the cost of prescription drugs to new highs for more Americans, according to a new report. Specifically, the estimated number of people in the U.S. who took medicines worth more than $50,000 annually rose 63% last year, to 576,000, up from 352,000 the year before. And the number of Americans who are estimated to be taking at least $100,000 worth of drugs jumped 193% to 139,000 people, from 47,000.

“The bottom line is that the number of people with very high prescriptions is increasing very rapidly,” says Glen Stettin, senior vice president for clinical research at Express Scripts, the pharmacy benefits manager, which reviewed data for 31.5 million people covered by commercial insurers, Medicare and Medicaid. “And a lot of people are being treated with expensive, life-long drugs and so they will be in this category for a long time.”